add version info to output files

[Reimar Bauer]

We should add a MSS version info to all output files if possible.

e.g. we could do by a XML Comment to the FTML file.

Having a version string of MSS enables later a migration path if we have to adopt output formats.

[Reimar Bauer]

Add a version field to FTML

Fix issue #259

→ <<cset 44ccd6e3eb4a>>